Limit Thermostat, Open On Rise, (250-40F) - 250F and below the electrical circuit will remain closed, 210F and up will open the electrical circuit,  thus 40 degree differential. 3/4"  For use on furnaces, dryers, fans, dishwashers, limits, ect., U.L.Rated, #L250-40. These limit thermostats are brand new and made by Smart Electric Corp.